selinux: fix setting of security labels on NFS

Before calling into the filesystem, vfs_setxattr calls
security_inode_setxattr, which ends up calling selinux_inode_setxattr in
our case.  That returns -EOPNOTSUPP whenever SBLABEL_MNT is not set.
SBLABEL_MNT was supposed to be set by sb_finish_set_opts, which sets it
only if selinux_is_sblabel_mnt returns true.

The selinux_is_sblabel_mnt logic was broken by eadcabc "SELinux: do
all flags twiddling in one place", which didn't take into the account
the SECURITY_FS_USE_NATIVE behavior that had been introduced for nfs
with eb9ae68 "SELinux: Add new labeling type native labels".

This caused setxattr's of security labels over NFSv4.2 to fail.

Cc: [email protected] # 3.13
Cc: Eric Paris <[email protected]>
Cc: David Quigley <[email protected]>
Reported-by: Richard Chan <[email protected]>
Signed-off-by: J. Bruce Fields <[email protected]>
Acked-by: Stephen Smalley <[email protected]>
[PM: added the stable dependency]
Signed-off-by: Paul Moore <[email protected]>

security/selinux/hooks.c

@@ -403,6 +403,7 @@ static int selinux_is_sblabel_mnt(struct super_block *sb)
 	return sbsec->behavior == SECURITY_FS_USE_XATTR ||
 		sbsec->behavior == SECURITY_FS_USE_TRANS ||
 		sbsec->behavior == SECURITY_FS_USE_TASK ||
+		sbsec->behavior == SECURITY_FS_USE_NATIVE ||
 		/* Special handling. Genfs but also in-core setxattr handler */
 		!strcmp(sb->s_type->name, "sysfs") ||
 		!strcmp(sb->s_type->name, "pstore") ||